This project deals with the cell and molecular biology of a newly described neuronal intermediate filament and its relationship to the neurofilament system. The ontogeny of peripherin and the neurofilament triplet proteins will be studies in mouse embryo using immunostaining. The relationship of these two filament systems in development will be examined with double- labeling, allowing construction of 3-D models. Interactions between the neurofilament triplet and peripherin will be investigated in an NF-rich, peripherin-negative system and in an NF-poor, peripherin-rich system, and in mixed systems; using double-labeling immunofluorescence staining and electron microscopy. The function of peripherin in neuronal differentiation will be studied by transfection of PC12 cells with specific DNA sense and anti-sense constructs. The regulation of expression of the mRNAs for peripherin and the neurofilament triplet protein by nerve growth factor will be examined in PC12 cells using 32P- labelled cDNA probes. The results of these studies will give insight into the roles of these two different filament systems in neuronal function and differentiation. The role of peripherin in neurological diseases will be investigated in model systems for neurodegenerative disorders and in human neuropathological specimens of motor neuron disease.